1 Technical Field
The present invention relates generally to a gas ventilation system for internal combustion engines, and more particularly to an improvement on a gas ventilation system designed to keep free from oil contained in the blowby gas to a throttle valve of an engine.
2 Background of Related Art
Blowby gas ventilation systems are known in the art wherein blowby gas in a crankcase of an engine is recirculated to an intake pipe for avoiding escape thereof to the atmosphere. FIGS. 1 and 2 shows one example of such blowby gas ventilation systems.
The surge tank 2 is tapered at an upstream side. The throttle body 1 having disposed therein the throttle valve 3 is connected to the surge tank 2. The blowby gas ventilation pipe 5 extends horizontally to the surge tank 2 to open into a tapered wall of the surge tank 2 immediately downstream of the throttle valve 3.
When the open of the throttle valve 3 is small at a lower engine load, intake air, as shown in FIG. 1, flows out of the throttle valve 3 at high speed through small clearances between an inner wall of the throttle body 1 and upper and lower peripheral portions of the throttle valve 3, thereby causing the pressure behind the throttle valve 3 to be decreased to produce strong swirls in that place. These swirls will cause the blowby gas entered from the ventilation pipe 5 to be attracted to the throttle valve 3, thereby causing oil contained in the blowby gas to stick to the throttle valve 3, resulting in oil deposit leading to a failure in a valve operation. Additionally, the backflow to the throttle valve 3 also occurs in horizontal plane as shown in FIG. 2, causing the blowby gas to flow behind the throttle valve 3 so that oil sticks thereto.
Japanese Utility Model First Publication No. 56-161166 teaches a blowby gas ventilation pipe which opens into a cylindrical wall of a venturi disposed within a portion of an intake pipe downstream of a throttle valve for achieving sufficient recirculation of the blowby gas even when the throttle valve is almost closed. This structure however also has the above drawbacks.
Further, in a multi-cylinder engine, the blowby gas entering the surge tank 2 flows into intake pipes 23 connected to a side wall of the surge tank 2 without being mixed with intake air sufficiently, thereby resulting in a variation in the quantity of the blowby gas entering the various cylinders of the engine, thus leading to variations in air-fuel ratio and oil flow to the cylinders.